[karticam]

This is PR 8 of a series of PRs to implement move semantics for plasma objects in core.

The complete design doc is here: https://docs.google.com/document/d/1ZJhgRmwVyKfNCR21CWf6xMcc0B6HJwSPQsfebTRvnnE/edit?tab=t.0#heading=h.7wcod1f9afpg

Until now _consume_once=True was rejected on streaming generator actor methods (#66620). With this PR it is accepted, and every object the generator yields can be moved to exactly one consumer, the same way a plain return can.

Changes

1. The generator object carries a flag. A streaming generator task has one return: the generator object. The objects it yields don't exist yet when the task is submitted. So AddPendingTask doesn't make the generator object MOVABLE. Instead it sets a new Reference field, yields_consume_once_, on it when a streaming generator object is created with _consume_once method option, through a new AddOwnedObject parameter. The generator object itself stays NOT_MOVABLE.
2. Each yielded object is created MOVABLE. OwnDynamicStreamingTaskReturnRef passes MOVABLE as the initial move state when the generator object has the flag. Every creation path goes through it.
3. The rejection is lifted. ActorMethod._remote no longer rejects streaming generator methods.

Nothing else changes for the generated object refs. Everything in the previous PRs apply to it.

Every yield of the generator becomes consume-once, including small ones kept in the owner's memory store.

A generator that runs again, after an actor restart or for lineage reconstruction, reports every item again, and the owner records the new run's node as each item's primary. For an item that was already moved, the consumer's node keeps its copy too, so the item has two copies until it goes out of scope. Master does the same today with the old copy of any item a generator reports again, so this PR doesn't change it.

[gemini-code-assist]

Code Review

This pull request implements support for consume_once on streaming generator actor methods in Ray. Previously, _consume_once=True was not supported for streaming generators. With these changes, each object yielded by a streaming generator with consume_once enabled is created as MOVABLE (allowing it to be moved to the consumer's node and freed from the producer's node), while the generator object itself remains NOT_MOVABLE. The implementation updates the C++ ReferenceCounter and TaskManager to track and propagate the yields_consume_once property, and adds comprehensive unit and integration tests in both Python and C++ to verify the behavior. There are no review comments to address, so no further feedback is provided.

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